Engine braking or retarder systems are often used to assist and supplement wheel brakes to slow heavy vehicles, such as tractor-trailers. Engine braking systems convert the vehicle engine into a power consuming air compressor by opening one or more of the engine exhaust valves during compression strokes of the engine. In order to accomplish this result, one or more actuators are provided to contact and move either the exhaust valves directly or valve opening apparatus, such as a crosshead or rocker arm, coupled to the exhaust valves.
Freiburg et al. U.S. Pat. No. 5,365,916 discloses an engine braking system wherein a slave piston is disposed adjacent a pivoting engine exhaust valve rocker arm. The slave piston includes a foot adapted to engage a flat surface which is machined on the rocker arm. The foot is capable of swiveling to accommodate the changing orientation of the flat surface as the slave piston extends and pivots the rocker arm.
While the Freiburg et al. device may be effective to open exhaust valves at desired times to accomplish engine braking, the use of a machined surface on the rocker arm results in the need for an undercut or relief in a portion of the rocker arm so that sufficient clearance is provided for the machining apparatus. This portion of the rocker arm is subjected to high forces during engine operation resulting in stress concentrations that can cause reliability problems. Also, the engine brake system is relatively tall, thereby limiting the potential applications for the braking system.